Nitrous oxide systems (NOS) for vehicles are designed to temporarily boost the power output of internal combustion gas engines. Such a system injects vaporized nitrous oxide into the intake of a gasoline engine to allow for a more energetic combustion stroke than would otherwise be available during normal operation, with greater power being transferred back to the piston and drive shaft with an ultimate increase in the horsepower output of the engine. The nitrous oxide is typically stored as a compressed liquid inside a pressurized bottle which is allowed to flash into a vapor upon release into the engine intake.
Similarly, water/methanol systems are designed to temporarily boost the power output of internal combustion diesel engines. Such a system injects a water/methanol mixture into the intake of a diesel engine. A liquid pump is used to inject the mixture of water/methanol into the intake system.
While both types of injection systems are designed to temporarily boost the power output of internal combustion engines, the two processes are generally considered to be incompatible, with the water/methanol system lending itself more to diesel engines while NOS injection is more compatible with gasoline engines using spark ignition. The two systems also employ substantially different processes. In the case of a water/methanol injection system, the water's ability to absorb latent heat during evaporation cools the incoming charge of air, creating a denser charge of intake air that contains the extra oxygen for combustion. The methanol acts as an alternative fuel source that can be combined with the extra oxygen to create a more energetic combustion stroke, while at the same time reducing exhaust gas temperatures (EGT). In the case of a NOS injection system, the vaporized nitrous oxide itself contains the additional oxygen that allows extra fuel to also be injected into the combustion chamber, also resulting in a more energetic combustion stroke.
One common characteristic for effective operation of both injection systems, however, is that a balanced air/fuel (or oxidizer/fuel) mixture flowing into the engine should be properly maintained throughout the boost phase. This can be difficult, because a precise increase in fuel or methanol must be provided to balance the additional oxidizer (in the form of vaporized nitrous oxide or a denser charge of intake air), which in turn can be difficult to measure and control.
A frequent problem with nitrous oxide injection systems is that the pressure inside the pressurized bottle can decrease with use and therefore proportionately less nitrous oxide is provided per release valve setting. Compounding the fuel/oxidizer balancing issue is the cooling effect that the compressed nitrous oxide liquid also has on the intake air as it is released into the engine's intake system, reducing the intake air's temperature and increasing its density. While this can provide even more oxidizer (i.e. oxygen) to the engine and enhance the power charging aspects of the nitrous oxide system, it can also upset the delicate balance of oxygen and fuel and can lead to an excessively lean mixture flowing into the combustion chamber.